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Abstract

Detailed biological analyses (e.g. epidemiological, genetic) of animal health and fitness in the field are limited by the lack of
large-scale recording of individual animals. An alternative approach is to identify immune traits that are associated with
these important functions and can be subsequently used in more detailed studies. We have used an experimental dairy
herd with uniquely dense phenotypic data to identify a range of potentially useful immune traits correlated with enhanced
(or depressed) health and fitness. Blood samples from 248 dairy cows were collected at two-monthly intervals over a 10-
month period and analysed for a number of immune traits, including levels of serum proteins associated with the innate
immune response and circulating leukocyte populations. Immune measures were matched to individual cow records
related to productivity, fertility and disease. Correlations between traits were calculated using bivariate analyses based on
animal repeatability and random regression models with a Bonferroni correction to account for multiple testing. A number
of significant correlations were found between immune traits and other recorded traits including: CD4+:CD8+ T lymphocyte
ratio and subclinical mastitis; % CD8+ lymphocytes and fertility; % CD335+ natural killer cells and lameness episodes; and
serum haptoglobin levels and clinical mastitis. Importantly these traits were not associated with reduced productivity and,
in the case of cellular immune traits, were highly repeatable. Moreover these immune traits displayed significant betweenanimal
variation suggesting that they may be altered by genetic selection. This study represents the largest simultaneous
analysis of multiple immune traits in dairy cattle to-date and demonstrates that a number of immune traits are associated
with health events. These traits represent useful selection markers for future programmes aimed at improving animal health
and fitness.